Hydraulic impact apparatus



Dec. 30. 1969 Filed Feb. 20, 1968 HYDRAULIC SIGNAL R. E. WE SUTERLUND ET AL HYDRAULIC IMPACT APPARATUS 2 Sheets-Sheet 1 HYDRAULIC PUMP FIG.]

FIG 2 INVENTORS Robert E Westerlund Herbert A, Westerlund Attorneys R. E. WESTERLUND ETAL HYDRAULIC IMPACT APPARATUS Dec. 30, 1969 Filed Feb. 20, 1968 .4 7 FIG 3 x54; ZZZ, /T-

'FIG 4 HYDRAULIC PUMP 2 Sheets-Sheet 2 INVENTOR5 Robert E. Westerlund gierbert A. .Westerlund Attorneys United States Patent 3,486,568 HYDRAULIC IMPACT APPARATUS Robert E. Westerlund, 2737 W. Mequon Road, Mequon, Wis. 53092, and Herbert A. Westerlund, Rte. 1, Box 450A, Port Washington, Wis. 53074 Filed Feb. 20, 1968, Ser. No. 706,904 Int. Cl. E21c 11/00, 9/00; E01c 19/30 US. Cl. 173-31 15 Claims ABSTRACT OF THE DISCLOSURE This disclosure relates to a hydraulically actuated impact apparatus.

A piston is slidably mounted in a housing and connected to a compaction plate. The housing includes a coaxial liquid inlet passageway aligned with the piston head. An annular valve ring is slidably disposed within an annular valve chamber encircling the piston and defines the side wall of the pressure or piston chamber. The valve ring includes a collection recess and a plurality of equicircumferentially spaced flow ports to interconnect the chamber between the head and the piston to an annular exhaust chamber which includes an exhaust port in the outer wall of the housing. A pair of diametrically spaced passageways are interconnected to the upper end of the valve chamber and a pressure signal source to continuously bias the valve ring downwardly to align the ports with the piston in such a manner as to seal the flow passageway to the outlet recess. Return signal pressure passageways are interconnected to the opposite end of the valve chamber and to the inlet port to raise the valve ring and provide full flow with the piston in the expanded work position to store energy. The signal source moves the ring downwardly and rapidly closes the flow path therebetween. The rapid flowing liquid is rapidly decelerated and generates a high pressure pulse on the piston and attached work member.

Alternatively, a spool valve is provided to alternately establish and block flow in a passageway which is connected by a port to a piston chamber.

This invention relates to hydraulically actuated impact apparatus and particularly cyclically imparting a sharp and heavy impact to a tool or work member.

Hydraulically operated industrial tools are employed for various purposes. Thus, air and liquid actuated wrenches and hammers have been suggested wherein the driving force is established by applying a working fluid to a piston-like element to establish a working force. In many applications a force transfer piston is employed wherein the piston is retracted under any suitable means and then a high pressure hydraulic force is applied to impart kinetic energy into the piston which upon striking a work member transfers the energy thereto as in impact force. Alternatively, for example, pile drivers have been suggested where in a hydraulic cylinder is employed to lift an impact tool and then hydraulic pressure is applied to the opposite end to rapidly drive the piston and the attached pile driver downwardly to establish impact engagement.

The present invention is particularly directed to a hydraulically actuated impact apparatus having a special hydraulic system to provide a working force from a hydraulic hammer effect which is specifically created by the intermittant establishment and termination of flow through a working chamber one surface of which constitutes a moveable work transfer member. The transfer member can be interconnected to any desired impact device. The present invention can be applied to any industrial impact tool such as the conventional pile drivers, earth compactor, pavement breaking drill or hammers and the like.

- 3,486,568 Patented Dec. 30, 1969 Generally, in accordance with the present invention a moveable or work transfer member forms a moveable component of a chamber which communicates with a flow passageway means between a suitable hydraulic system to pass liquid through the passageway means. A valve means is associated with the outlet side of the flow passageway and interconnected to rapidly close and terminate flow. The rapid close off of the flow results in a corresponding deceleration of the flowing liquid with a resulting high hydraulic pressure impulse 'in the-chamber which is also applied to the transfer member. The present invention is therefore based on the concept of establishing an interrupted flow to produce hydraulic work or forces.

In accordance with a preferred construction of the present invention, the transfer member constitutes a piston having a piston shaft extending from the chamber and forming a coupling to an operating or work member. The piston is slidably mounted within a pressure chamber having a coaxial liquid inlet passageway aligned with the piston. An annular valve ring is slidably disposed within an annular valve chamber encircling the piston for coaxial movement relative to said piston. The valve ring defines the side wall of the pressure or piston chamber and is generally disposed in a liquid-tight sliding engagement with the side wall of the piston. The valve ring includes a plurality of flow passageways and preferably a collection recess adjacent the piston to interconnect the portion of the chamber between the head and the piston to an outlet or exhaust passageway formed in the outer portion of the housing. A signal pressure passageway is interconnected to the upper end of the valve chamber to continuously bias the valve ring toward a given end of the chamber aligning the collection recess and ports with the piston in such a manner as to seal the inlet passageway from the outlet passageway. Return signal pressure passageways are interconnected to the opposite end of the valve chamber for moving the valve ring to the opposite end of the valve chamber and aligning the valve ports with the portion of the piston chamber above the piston to permit essentially free liquid flow therethrough. In operation the piston will be in the generally expanded working position and the valve ring in the raised or full flow position under which conditions the hydraulic liquid freely flows between the inlet port passageway and the outlet passageway and stores substantial energy in the flowing liquid or fluid. The pressure signal applied to the upper end of the valve ring causes it to move downwardly toward the piston and rapidly closes the flow path there between. As a result the flowing liquid is rapidly decelerated and generates a high pressure pulse on the piston and attached work member. The return pressure signal may be taken from the main inlet passageway such that the sharp pressure impulse applied to the piston is simultaneously applied to the annular valve ring causing it to return to the full flow position. The pressure in the chamber decreases as a result of the reestablishment of the flow path and allows the piston to return to a raised position. The piston and the valve ring will tend to move in the opposite direction to more rapidly establish and terminate the flow sequence to form a series of rapid working impact impulses.

The drawings furnished herewith illustrate preferred constructions of the present invention in which the above advantages and features are clearly disclosed as well as others which will be readily understood from the following description.

In the drawing:

FIG. 1 is an elevational view of the present invention applied to an earth compacting tool or device with parts broken away and sectioned to show inner detail of construction;

FIG. 2 is a top plan view of FIG. 1 with parts broken away to show further details of construction;

FIG. 3 is a fragmentary view taken on line 33 of FIG. 2; and

FIG. 4 is a partial view showing an alternative construction.

Referring to the drawing, the present invention is applied to a soil or earth compaction device for purposes of clearly and fully explaining the operation of a preferred construction of the invention. However, such a particular application is not considered limiting in connection with the broadest aspects of the present invention.

In the illustrated embodiment of the invention, a soil compaction plate 1 is adapted to rest on the soil and is interconnected to a piston 2 which is slidably disposed within a housing unit 3. A support plate 4 is interconnected to the lower end of the unit 3 and interconnected at the outer ends by a plurality of resilient attachment assemblies 5 to the corresponding outer end portions of the plate 1 to interconnect and support the plate and the piston 2 to the unit 3. The resilient coupling assembly 5 permits limited movement of the plate 1 with respect to the support plate 4 as more fully developed hereinafter.

The housing unit 3 includes an inlet passageway or port 7 aligned with the outer face or the top of the piston 2 and connected to a Suitable source 8 of a pressurized oil or other suitable hydraulic liquid. An outlet passageway or port 9, shown on the left side of the unit 3, is interconnected to a suitable hydraulic sump 9a or the like. An annular valve member 10 encircles the piston 2 and cooperates therewith to open and close the outlet passageway 9 with respect to the flow of the hydraulic liquid from the inlet passageway 7.

In operation, the liquid from pump 8 is allowed to rapidly flow through the cylinder unit 3 such that kinetic energy is stored in the flowing liquid. The valve member 10 is then moved to rapidly close the passageway 9 such that the deceleration of the liquid in passageway 7 results in hydraulic hammer action and high impulse forces on the piston 2 which are transmitted directly to the compaction plate 1, in the illustrated embodiment of the invention.

More particularly, the illustrated housing unit 3 is a laminated or multiple unit construction including an upper wall 11 and a lower wall 12 interconnected by an intermediate tubular side wall 13 which is clamped therebetween to define a piston chamber 14 within which the piston 2 is slidably disposed. A plurality of nut and bolt assemblies 15 interconnects the four corners of the several walls to provide a rigid and fluid tight housing.

The upper wall 11 is a rectangular block-like member having a central reduced cylindrical portion 16 which projects into the tubular sidewall 13 and toward the bottom sidewall 12.

The inlet passageway 7 is formed concentrically of the piston chamber 14 in the upper wall 11 with the other edge curved to provide a smooth flow into the piston chamber. The reduced portion 16 is of a diameter corresponding to that piston 2 to define the upper portion of the valve chamber 17 which extends completely about the piston chamber and to the opposite side thereof and within which valve member 10 is mounted.

The lower wall 12 is centrally apertured or bored to receive a tubular piston shaft 18 integrally formed to the back side of the piston 2. The lower wall otherwise is generally similar to the upper wall and includes an inner projecting portion 19 generally corresponding to the reduced portion 16 and similarly projecting inwardly to define the bottom of the piston chamber 14 as well as the lower portion of the valve chamber.

The side wall 13 includes an inner wall concentric with the projecting portions 16 and 19 and the piston 2 to form the outer wall of the valve chamber 17. The side Wall 13 includes an annular collection chamber 20 on its inner peripheral surface for collecting the liquid from the piston chamber 14 and directing it through the outlet passageway 9.

Valve member 10 is an annular valve ring slidably mounted within the annular valve chamber 17 defined by the projecting portions 16 and 19 of the upper and lower walls 11 and 12 and the piston 2. The valve ring 10 has an axial length somewhat less than the depth of the valve chamber 17 to permit sliding and coaxial movement with respect to the piston 2 for purposes more fully described hereinafter. The inner face of the valve ring 10 includes an annular collecting recess 21 and a plurality of equicircumferentially distributed ports 22 in the base of the recess to permit liquid flow from the piston chamber 14 to the collection chamber 20 of the sidewall 13.

In the illustrated position, the valve ring 10 is in a raised flow position and the piston 2 is in an extended position with a relatively unrestricted passageway from the inlet passageway 7, laterally through the piston chamber 14 to collection recess 21 and through ports 22 of the valve ring to the outlet collection chamber 20 and port 9. Under this condition, a relatively high rate of hydraulic liquid flow is established therethrough. If the valve ring 10 is moved down to rapidly close off the passageway, the flowing liquid is rapidly decelerated and generates a high pressure pulse which is applied directly to the head of the piston and causes it to move outwardly to effect a work function. The piston head may be provided with a spherical recess 23 in the outermost face as shown.

In the illustrated embodiment of the invention, the valve ring 10 is hydraulically positioned. A pair of hydraulic signal passageways 24 and 25 are provided in alignment with diametrically opposite portions of the valve chamber 17 and are interconnected in common to a suitable hydraulic signal source 26 which may be connected through a suitable signal supply system to the hydraulic pump 8. The signal applied to the passageways 24 and 25 will provide a balance downward force on the ring and move the annular valve member 10 downwardly to the lower end of the valve chamber 17 to close otf the previously described fiow passageway. An annular resilient cushion 27 is provided in the bottom of the valve chamber to prevent metal to metal engagement of the valve ring on the lower wall. By providing a rapid movement of the valve ring relative to the piston, the flow can be terminated very rapidly in order to establish a desired hydraulic hammer effect.

The valve ring 10 is raised to again establish the flow passageway by applying the pressure pulse in the passageway 7 to the underside of the valve ring 10. A pair of signal passageways 29 and 30 extend through the upper wall 12 and particularly from the inlet passageway and then downwardly through the intermediate wall 13 to 1 the lower portion of the valve chamber 17. As a result when the flow is terminated and the hydraulic pressure impulse is created, the pressure signal is simultaneously transmitted through the passageways 29 and 30 to return the valve ring 10 to the full flow position.

As a result, the valve ring 10 will tend to continuously reciprocate within the valve chamber 17 resulting in rapid opening and closing of the flow passageway and with a simultaneous series of hydraulic hammer effects.

Further, the piston will tend to move in the opposite direction from the valve ring 10. This will increase the rapidity of the opening and closing of the flow passageway.

The downward piston movement is cushioned by a suitable resilient ring 31 secured within a suitable recess on the inner edge of the lower wall 12. The ring 31 slidably engages the shaft 18 which projects outwardly through the wall,

The outer end of the tubular piston shaft includes an internally threaded portion to receive a clamping bolt 32 which secures a washer 33 to the outer end of the piston shaft 18 to define a cushion supporting flange. An annular or doughnut shaped cushion 34 of rubber or a y resilient rubber-like material encircles the piston shaft between the washer 33 and the bottom wall of the housing unit 3. A suitable small ring spacer 35 is shown disposed between the cushion 34 and the shaft 18 to laterally support the cushion 34 and to limit the return movement of the piston so as to prevent striking of the opposed chamber wall.

The piston shaft 18 is coupled to the compaction plate 1 through an enlargement 36 on the backside of the plate 1 upon which the bolt head rests. The bolt head and enlargement are formed with complementing semi-spherical surfaces, as at 37, to allow pivotal movement therebetween. The enlargement 36 can be integrally formed as illustrated or separately formed and interconnected to the plate in any suitable manner. In the illustrated embodiment of the invention, a circular guide wall 38 is secured to the edge of the enlargement 36 and projects upwardly about the washer 33 and cushion 34 to guide the compaction plate movement.

The compaction plate 1 is formed in accordance with the usual construction and includes upwardly bent or raised leading and trailing ends. A plurality of strengthening braces 39 is secured between the circular wall 38 and the corners adjacent the bent portion.

The support plate 4 to which the compaction plate 1 is resiliently secured is formed of a somewhat smaller length and with similar shaped ends. The plate 4 includes a central opening through which a reduced portion of the lower wall 12 extends.

The resilient coupling assemblies 5 each include a first resilient spacer 40 disposed between the support plate 4 and compaction plate 1. A bolt 41 extends through the plates and the spacer 40 and is secured to the compaction plate 1 in any suitable manner such as the clamping nut 42 to resiliently interconnect the compaction plate 1 for movement relative to the support plate 4. A resilient spacer 43 encircles the bolt 41 between the upper surface of the support plate 4 and a washer 44 which is deposed between the spacer and the head of the bolt 41. As a result, the compaction plate 1 is allowed limited movement with respect to the support plate 4.

The operation of the illustrated embodiment may be briefly summarized as follows:

The signal passageways 24 and 25 are connected to the hydraulic signal source 26, the hydraulic pump 8 is inter connected to the inlet passageway 7 and the outlet passageway 9 to sump 9a, Initially, the pressure of source 26 will move the valve ring downwardly to close the flow path or passageway. The pressure in the inlet port 7 will increase and rise above the level of source 26 to move the ring 10 above the piston level to establish flow. The pressure in port 7 will tend to move the piston 2 downwardly. Flow of liquid through the piston chamber 14 is thus permitted by the raised valve ring 10 which spaces the cutoff edge 45 of the valve ring 10 from the head of the piston, and energy is stored in the liquid. The pressure at port 7 drops and the hydraulic signal of source 26 then moves the valve ring 10 downward until the cutoff edge 45 engages the piston 2 at which time the flow is completely terminated. This generates a high pressure impulse which drives the piston 2 downwardly to do work and drives the valve ring 10 upwardly. This again spaces the cutoff edge 45 from the piston 2 with a resultant reestablishment of flow. The source pressure of source 26 is again suflicient to drive valve ring 10 downwardly to establish a corresponding cycle. Further, the piston 2 will simultaneously move upwardly while the valve ring 10 moves downwardly to rapidly close off the flow such that substantial pressure impulses the corresponding heavy impact movement of piston 2 is obtained.

When the valve ring 10 is positioned to close the flow passageway between the inlet port and the outlet port, the very substantial impulse forces established are also impressed upon the adjacent inner surface of the valve ring 10. If desired, one or more small hydraulic pressure balancing openings 46 may be provided in the ring 10, as

shown in FIG. 1, immediately outwardly of the ring recess 21. With the ring 10 in a flow interruption position, the openings are aligned with the pressure chamber and the hydraulic impulses will be transmitted to the outer wall of the valve chamber 17 and the forces across the valve ring essentially balanced.

The first couple of cycles will normally be relatively weak until the movement of the valve ring 10 and the piston 2 are such as to substantially open the valved passageway and permit reasonably substantial liquid flow.

Although the illustrated flow passageway is partially defined by the working chamber, the flow path may be removed as long as communication with a working member is maintained. For example, an alternative construction is shown in FIG. 4 and described as follows.

Referring particularly to FIG. 4, the alternative embodiment of the invention includes a piston 47 slidably supported within a piston chamber 48. A piston rod 49 extends outwardly therefrom for interconnection to any suitable work member, such as a hammer, not shown. A transfer port 50 to the piston chamber 48 extends coaxially outwardly through a spool valve assembly 51 to an inlet port 52 for connection to a suitable hydraulic pump or other source of hydraulic liquid, as in FIG. 1. The spool valve assembly 51 selectively interconnects the inlet port 52 with an outlet port 53 disposed to one side of the inlet port 52. The system operates in basically the same as that of the previous embodiment. With the spool valve assembly 51 open, flow is established and a relatively low pressure condition is present in the inlet port 51 and the transfer port 50. When the spool valve assembly closes, flow is terminated and shock forces are generated in the inlet port 52 which are transmitted through the communicating or transfer port 50 to the piston chamber 48 and to piston 47.

More particularly, the illustrated spool valve assembly 51 includes a housing 54 suitably interconnected to the upper end of the working piston assembly housing 54 and having the port 50 coaxially aligned with the inlet port 52. The housing 54 includes a cylindrical valve chamber extending laterally therethrough with the opposite ends of the valve chamber closed by end plates 55 and 56. A tubular valve spool 57 is slidably disposed within the valve chamber for lateral movement relative to the ports 52 and 53. The valve spool 57 includes an annular central recess 58 having a rectangular cross-section generally aligned with the inlet port 52. The outlet port 53 is disposed to the right side of the inlet port 52, as viewed in FIG. 4, and is connected thereto by annular collecting chamber 59 encircling the valve spool and the opening 60 in the wall 61 therebetween. When the valve spool 59 is disposed to the right as illustrated in full lines in FIG. 4, the right edge 62 of the recess 58 moves into the outlet chamber 59 and establishes a relatively free flow passageway from the inlet port 52 to the chamber 59 and the outlet port 53. The valve spool 57 is moved to the left of FIG. 4 to close the passageway when the sharp edge wall 62 of the recess moves into the wall opening 60. By forming of the recess 58 with a relatively sharp edge wall 62, the outer edge constitutes a cut-off edge cooperating with the wall 61 to function generally in the same manner as the annular valve ring previously described with respect to the embodiment of FIGS. 1-3.

The valve spool 57 is fluid activated and is moved from the full line illustrated position to the left by a suitable fluid signal applied via a set line 63 to the right end face of the valve spool 57 which is provided with a correspondmg openlng.

The adjacent end of the valve spool 57 is generally telescoped over a member 64 integrally formed with the end plate 55 and having a corresponding end extending into the spool. A suitable sealing gasket 65 is disposed between the outer periphery of the member 64 and the inner periphery of the valve spool 57 to seal the passage therebetween.

A plurality of circumferentially distributed inclined openings 66 are formed in the end plate extending from the outer periphery of the member 64 to the opening in the end plate 55. The incoming signal line 63 is connected to the opening in the end plate 55 and applies a fluid pressure through the openings 66 to the end of the tubular valve spool 57.

The opposite end of the spool 57 is similarly mounted on a member 67 and a return signal line 68 is connected thereto to apply a return pressure to the opposite end of the valve spool 57.

By cyclically applying a set signal and a reset or return signal to the respective lines 63 and 69, the liquid flow through the spool valve assembly is alternately established and terminated. At each termination, hydraulic shock forces are generated and transmitted through the port 50 and chamber 48 to the piston 47 to provide high impact forces which can be applied to any desirable work function.

The present invention thus provides an improved impact generating apparatus which may be applied to any one of a substantial number of different tools or the like.

We claim:

1. A hydraulically actuated impact apparatus, comprisa flow passageway means for establishing a rapidly flowing liquid and having an inlet means and outlet means to define a high rate liquid flow path with the energy stored in the liquid,

an energy transfer means communicating with said passageway means, and

means to rapidly and selectively close said outlet means to cut 01f said liquid flow and thereby establish a high pressure impulse in said passageway means and on said energy transfer means.

2. A hydraulically actuated impact apparatus comprisa housing unit having a movable work member forming a part of a pressure chamber within said housing unit, said work member having a workng position and a non-working position,

said housing having an inlet port means and outlet port means for establishing a rapidly flowing liquid flow path therethrough in liquid communication with said pressure chamber, and

valve mean associated with said outlet port means to rapidly close said outlet port means with said work member in a non-working position and thereby gen erate hydraulic forces on said movable work member as a result of deceleration of the liquid in the inlet port side of said valve means to actuate said work member to the Working position.

3. The hydraulically actuated impact apparatus of claim 2,

wherein the movable work member is a piston slidably mounted in said pressure chamber,

said inlet port being coaxially aligned with said piston and said outlet port being disposed to one side of said chamber and including an annular recess encircling said piston with the liquid fiow path extending radially between the piston and the chamber, to said annular recess, and

said valve means is an annular valve member encircling said piston and having valve openings, and means to selectively position said annular valve member to close said flow path.

4. The hydraulically actuated impact apparatus of claim 2 having means to periodically move the valve means between open and closed position with respect to said outlet port.

5. The hydraulically actuated impact apparatus of claim 2 having a first hydraulic means to move the valve means to full flow position and a second hydraulic means to move the valve means to a stop flow position with respect to said outlet port.

6. The hydraulically actuated impact apparatus of claim 2 having said means connected to said inlet port and to said valve means to actuate said valve means and open said outlet port means in response to given action of said hydraulic force.

7. The hydraulically actuated impact apparatus of claim 2 wherein said work member is a piston slidably mounted in said chamber, said inlet port means and outlet port means being located between the head of the piston and the axial wall of the chamber, to establish the flow path, and a valve ring encircling said piston and movably axially in a valve chamber for selectively interrupting said flow path.

8. The hydraulically actuated impact apparatus of claim 2 wherein said work member is a piston slidably mounted in said chamber, said inlet port means and outlet port means being located between the head of the piston and the axial wall of the chamber, to establish the flow path, and a valve ring encircling said piston and movably axially in a valve chamber for selectively interrupting said flow path, and a signal pressure means coupled to said valve ring to position the valve ring in position to seal the flow path from the inlet port means to the outlet port means, and signal pressure passageways between the inlet port means and the valve chamber for return of the valve ring against the force of said signal pressure means to open said flow path.

9. The hydraulically actuated impact apparatus of claim 2 wherein said work member is a piston slidably mounted in said chamber and said housing having a head with said inlet port coaxially aligned with one end of said piston and a sidewall spaced from said piston to define an annular valve chamber, an outlet port being formed in said sidewall in communication with said valve chamber, a valve ring disposed within said annular valve chamber for coaxial movement with said piston and having a plurality of circumferentially distributed valve ports, said valve member defining the sidewall of said pressure chamber, a signal pressure passageway connected to one end of said valve chamber to bias the valve ring toward one end of the chamber to align the valve ports with the piston and seal the passageway from the inlet port to the outlet port, and signal pressure passageways to the opposite end of the valve chamber for moving the valve ring to the opposite end of the valve chamber to dispose the valve ports outwardly of the piston and establish flow from the inlet port through said outlet port.

10. The hydraulically actuated impact apparatus of claim 2 wherein said work member is a piston slidably mounted in said chamber and said housing having a head with said inlet port coaxially aligned with one end of said piston and a sidewall spaced from said piston to define an annular valve chamber, said outlet port being formed in said sidewall and having an annular recess adjacent said valve chamber, a valve ring deposed within said annular valve chamber for coaxial movement with respect to said piston, said valve member having a centrally located annular recess on the inner periphery with a plurality of circumferentially distributed valve ports, said valve member being in liquid tight sliding engagement with the piston and defining the sidewall of said pressure chamber, a signal pressure passageway connected to one end of said valve chamber to bias the valve ring toward one end of the chamber to align the valve recess with the piston and seal the passageway from the inlet port to the outlet port, and signal pressure passageways connected between the inlet port and the opposite end of the valve chamber for moving the valve ring to the opposite end of the valve chamber to dispose the valve recess and ports outwardly of the piston and in alignment with the pressure chamber to establish flow from the inlet port hrough said outlet port.

11. The hydraulically actuated impact apparatus of claim 10 wherein said valve ring includes hydraulic pressure balancing openings located outwardly of said annular recess, said openings balancing the lateral pressure on said valve. ring with the valve recess positioned to seal the passageway from the inlet port to the outlet port.

12. The hydraulically actuated impact apparatus of claim 3 wherein said valve member includes small pressure balancing openings aligned with the inlet port means with said valve member positioned to close the flow path.

13. The hydraulically actuated impact apparatus of claim 2 wherein said work member is a piston slidably mounted in said pressure chamber, a valve assembly mounted on said pressure chamber and having said inlet port means communicating with said pressure chamber.

14.- The hydraulically actuated impact apparatus of claim 2 wherein said work member is a piston slidably mounted in said pressure chamber, a valve assembly mounted on said pressure chamber and having said inlet port means communicating with said pressure chamber, said valveassembly being a spool valve construction having a valve chamber extending laterally of said input port means and a spool slidably mounted therein for selectively interrupting flow, and means coupled to said valve spool to position the valve spool in position to seal the flow path from the inlet port means to the outlet port means to return the valve spool to an alternate position to open said flow path, said valve spool being constructed and arranged to establish a rapid opening and closing of said flow path.

15. The hydraulically actuated impact apparatus of claim 2 wherein said Work member is a piston slidably mounted in said chamber and said housing having a head with transfer port coaxially aligned with one end of said piston, a spool valve assembly secured to the head and having an inlet port aligned with said transfer port and an outlet port formed to one side of said inlet port and having a laterally extending valve chamber, a valve spool slidably disposed within said valve chamber for axial movement and having an annular recess with a sharp edge, signal pressure passageways connected to opposite ends of said valve chamber for selectively moving the valve spool to position the valve recess connecting said inlet port to the outlet. port and to alternately seal the inlet port from the outlet port.

References Cited UNITED STATES PATENTS 486,774 11/1892 Gibbs 173125 X 95" 4,399 4/1910 Norcross 91328 1,785,998 12/1930 Brooke 9139 2,447,312 8/1948 Burt 91-50 3,411,592 11/1968 Montabert 9150 X ERNEST R. PURSER, Primary Examiner US. Cl. X.R. 

